Multi-layer flexible film structures are widely used in a variety of applications and products. They are often fabricated for use, for example, as packages in the food and medical industries, as electronic films such as Radio Frequency Identification (RFID), flexible circuits in the electronics industry and as display media and labels in the consumer markets. Many of the multi-layer film structures consist of one or more polymer films. Some include metal layers within the multi-layer structure. Each of these layers serves a specific purpose and when put together could improve the durability, printability, barrier characteristics, or other functionalities required for the targeted application.
Fabrication of products from multi-layer film structures can be a time consuming and costly process. Efficiency gained in improving fabrication techniques and methods can be advantageous in the marketplace. Lasers have been used in cutting and scoring of multi-layer film structures. The use of lasers allows the fabrication to be operated on a specific layer with speed and precision often not possible by other techniques. Laser fabrication can be very productive. Since laser beams can be steered by devices such as galvanometer scanners, beam processing speeds can reach 200 inches per second (ips). Also, the lasers can be digitally commanded, thus production speed can be met while material is continuously transported into the cutting zone and the cutting operation is performed on the fly. In the production of packaging films, production speeds from 30 to 300 meters per minute are common.
Laser scoring and laser cutting as used herein includes making notches, circles, lines, shapes, etc. in the layers of the multi-layer structure. Both laser scoring and laser cutting remove the structure of the layer at the desired site. Cutting results in notches, circles, lines, and shapes that go all the way through a layer or multiple layers. Scoring results in notches, circles, lines, and shapes that only penetrate partially through a layer or a multi-layer structure.
CO2 based lasers have been utilized for the cutting and scoring of materials having polymer layer or layers and the fabrication of products from such multi-layers. CO2 based lasers, however, are not effective when metal layers are present within the multi-layer structures because the metal layer in general has substantially different absorption properties than the polymer film layer. A sufficiently high powered CO2 laser can overcome the low absorption of metal and can cut through both polymer and the metal by continuously increasing the power or slowing down the cutting speed. While this can be done, it is generally not practical or economical because of the quality of the cut or the speed of production. In addition, it lacks finesse to achieve the fine features, such as in scoring, which is one of the important reasons why lasers are used. Short wavelength lasers, such as fiber lasers and Neodymium YAG lasers, have much higher absorption for the metal, but essentially have very low or no absorption for most polymers. In recent years, pico-second and femto-second lasers have become commercially available. These types of lasers, with sharp pulse density, often operate as “cold cutting” by ablating material independent of the material type. However, with the exception of using such as in micro-machining, this class of lasers still lacks overall power and is too slow for general manufacturing of products.
The common practice of scoring of a multi-layer structure having a metal layer and polymer film layers involves the use of two or more laser types to cut simultaneously or in tandem to form a common overlapping scoring line. A CO2 laser based laser system is often used to score the polymeric layer or layers and a fiber laser is used to score the metal layers. The use of two or more lasers to cut a common part has major disadvantages. In addition to the larger footprint of the equipment and additional supporting mechanical and electrical controls, a significant disadvantage is the level of precision and consistency that can be achieved when two laser lines are required to overlap to form a common cut or score. Consider the use of the two lasers to fabricate a common scoring line on the polymer layer and the metal layer with a cut width of 0.1 mm at a speed of 100 ips while the material is being transported. The precise alignment of the steering beam components for each of the lasers in order to provide overlapping of the two laser beams is time consuming. The stability of the overlap of the two beams will continuously be affected by the environmental conditions such as temperature changes and humidity variations. Monitoring these changes raises serious issues on frequency of quality inspection of the products, maintenance down time and productivity. When the two lasers are operated in tandem, material tension and fluctuation of transport speed also become important considerations. Processing of wider web multi-layer film, as often done in the factory, will require multiple pairs of the two-laser systems. In such cases, the difficulties in set-up and maintenance multiply, making production difficult, if not impossible. There is a need for a simpler laser system to score multi-layer structures having metal and polymer layers with one laser that can meet production requirements.